The present invention relates to a process for epoxidizing an allyl ether of an active hydrogen-containing compound, more specifically an aryl allyl ether, by contacting the aryl allyl ether with an inorganic oxidant, more specifically aqueous hydrogen peroxide, or with an organic oxidant, more specifically an organic hydroperoxide such as an alkyl or an aromatic hydroperoxide, in the presence of a transition metal catalyst effective to form an epoxide of the aryl allyl ether.
Aryl glycidyl ethers, commercially known as epoxy resins, are manufactured successfully on a large industrial scale and are widely used in a variety of industrial and commercial sectors. Two types of reactions have heretofore been known for making the epoxy moiety of aryl glycidyl ethers. In the first type of reaction, reactive hydrogen-containing molecules, such as phenol or polyphenols, alcohols, or carboxylic acids, are reacted with epichlorohydrin, with or without catalyst(s), under basic conditions to form glycidyl ethers or glycidyl esters. The glycidyl ethers made by the first type of reaction process may have a high organic chloride content which may be deemed as undesirable in some applications, for example, in electronic applications.
In the second type of reaction, an oxidant is utilized to directly epoxidize an allyl ether or allyl ester of the corresponding reactive hydrogen-containing organo compounds, such as alcohols, phenols or carboxylic acids. Some known oxidants useful in the second type of reaction include, for example, peracetic acid, hydrogen peroxide, dimethyldioxirane, and peroxyimidic acid.
U.S. Pat. No. 5,578,740 discloses known epoxidation processes to epoxidize aryl allyl ethers. The epoxidation processes include reacting the allyl ethers with a peroxygen compound such as peracetic acid and hydrogen peroxide in the presence of catalytic system such as Na.sub.2 WO.sub.4 /H.sub.3 PO.sub.4 /quaternary ammonium salt, wherein the quaternary ammonium salt is for example, trioctylmethylammonium nitrate.
Because of the cost of the above known oxidants, the side reactions of epoxidation, or the difficulty of the purification processes associated with the above allyl ether and/or allyl ester epoxidation methods, none of these epoxidation methods using oxidants heretofore known are commercially viable for the production of large volume, basic chemicals.
Another known process for the formation of an epoxide uses organic oxidants, such as an organic hydroperoxide, for making propylene oxide via oxidation of propylene in the presence of a transition metal catalyst. This reaction is limited to the epoxidation of activated or electron-rich aliphatic or cycloaliphatic alkenes such as propylene, cyclohexene, and octene-1. In this known method, including the process currently being used for making propylene oxide on a large industrial scale, the limiting amount of reagent is the oxidant, and propylene is used in substantial excess. The overall conversion of propylene to epoxide is low (for example, less than 50 percent) based on propylene used. Therefore, a separation process through fractional distillation is used to easily separate the product propylene oxide from unreacted propylene, and the unreacted propylene is then recycled to the reactor used in the epoxidation reaction process.
U.S. Pat. No. 5,118,822 issued to Shum et al., discloses a process for epoxidizing olefins, including monomeric allyl phenyl ether, to epoxide compounds by contacting the olefins with organic hydroperoxides in the presence of a rhenium oxide salt catalyst comprised of perrhenate anions and organopnicogen-containing counter cations. Shum et al., do not disclose the use of a ligand-containing catalyst and do not report a yield for phenyl glycidyl ether. It is undesirable to have such an acidic, high oxidation state, perrhenate anion since such a perrhenate anion may be a catalyst which may promote epoxide ring hydrolysis.
U.S. Pat. No. 5,319,114 discloses a process for epoxidation of olefins including phenyl allyl ether by reacting an organic hydroperoxide in the presence of a heterogeneous catalyst comprised of a carbon molecular sieve containing a transition metal oxide, such as molybdenum trioxide. In U.S. Pat. No. 5,319,114, the transition metal is entrapped on the carbon through absorption and no stable chemical bond is formed between the transition metal oxide and the carbon molecular sieve. Thus, the active form of the catalyst is molybdenum trioxide which is ineffective for providing high epoxidation yields of phenyl allyl ether. There is no yield reported for phenyl allyl ether in U.S. Pat. No. 5,319,114.
U.S. Pat. No. 5,633,391 issued to Fenelli, S. P., discloses a process for the epoxidation of olefins, including monomeric phenyl allyl ether, by contacting the olefin with bis(trimethylsilyl)peroxide as the oxidant in the presence of a rhenium oxide catalyst in an organic solvent. The conversion of phenyl allyl ether to phenyl glycidyl ether using the process disclosed by Fenelli is low (36 percent) and bis(trimethylsilyl)peroxide is expensive and not available on a commercial scale. Without the presence of an organic basic additive in the epoxidation process described in U.S. Pat. No. 5,633,391 using a rhenium catalyst, the phenyl glycidyl ether epoxide will quickly decompose and hydrolyze to a glycol.
Furthermore, it was found that a low yield of epoxidation by the catalysts disclosed in U.S. Pat. Nos. 5,118,822; 5,319,114 and 5,633,391 is obtained and therefore the processes disclosed in these patents would be difficult to apply in the epoxidation of aryl allyl ethers, because most allyl ether substrates and the epoxidation products thereof having commercial value are high boiling point compounds. Therefore, the use of the processes and catalyst systems disclosed in U.S. Pat. Nos. 5,118,822; 5,319,114 and 5,633,391 are limited because of the difficulty in separating reactant from the product to permit reactant recycle.
Great Britain Patent No. 2,309,655 discloses a process for making heterogeneous catalysts comprised of an inorganic molecular sieve containing a transition metal useful for oxidations of alkenes, including epoxidations of alkenes, with hydrogen peroxide or an organic hydroperoxide. However, the heterogeneous catalysts claimed in GB 2,309,655 lack selectivity which results in low epoxidation yields, therefore requiring excess olefin to be used. The heterogeneous catalysts of GB 2,309,655 are also known to be very acidic and the use of such acidic catalysts results in the ring opening hydrolysis of an epoxide product forming an undesired glycol product. Furthermore, no data is given for any type of epoxidation reaction with aryl allyl ethers in GB 2,309,655.
Therefore, it would be desirable to provide a process for epoxidizing aryl allyl ethers without the disadvantages of prior known processes, to provide high conversions of the aryl allyl ether, and to provide high yields of epoxidation with good selectivity of organic oxidant.